Justification:
This species has been intensively fished since the early 1950s. Its generation length is conservatively estimated to be 12 years. Estimated spawning stock biomass has declined approximately 85% over the past 36 years (1973–2009) and there is no sign that the spawning stock is rebuilding. It is therefore listed as Critically Endangered. Implementation of effective conservation and management measures are urgently needed.

This species is found in the Atlantic, Indian and Pacific oceans. It is found in temperate and cold seas, mainly between 30°S and 50°S, to nearly 60°S. During spawning, large fish migrate to tropical seas, off the west coast of Australia, up to 10°S.

Worldwide reported landings show a gradual, but variable, increase from 13,552 tonnes in 1952 to a high of 55,200 tonnes in 1969, and then gradually decreasing, to 12,122 tonnes in 1991. Catches from 1992 to 2006 have been relatively stable, averaging around 16,0000 tonnes per year (FAO 2009). This species is farmed in Australia, where mostly immature fish (age 2–4 years) are removed from the wild and fattened in farms. This complicates estimation of catches and is associated with high mortality rates of fish during transport.

A stock assessment has been carried out by the Commission for the Conservation of Southern Bluefin Tuna (CCSBT 2006). Based on the median results of this most recent stock assessment, there has been an estimated 85.4% decline in spawning stock biomass over the past 36 years from 1973 to 2009 (CCSBT 2010).

By maturity, most Southern Bluefin Tuna lead an oceanic, pelagic existence. Spawning fish and larvae are encountered in waters with surface temperatures between 20 and 30°C. This species is an opportunistic feeder, preying on a wide variety of fishes, crustaceans, cephalopods, salps, and other marine animals.

Maximum size is 225 cm fork length (FL) and 200 kg. Longevity is 20 or more years. Sex ratio in catches shows that as juveniles, females outnumber males but this situation is reversed in adults. Maturity can occur at 120 cm (FL) but more commonly at 130 cm or about eight years old; size at 50% maturity has also been estimated to be 152 cm (FL) (Collette and Nauen 1983, Thorogood 1986, Caton 1994, Farley and Davis 1998, Schaefer 2001, Collette 2010). Based on the CCSBT (CCSBT 2009, CCSBT 2010), age of first maturity is estimated to be about 10 years and longevity about 40 years. Generation length is therefore very conservatively estimated to be at least 12 years.

Spawning is restricted to a relatively small area off northwestern Australia in the eastern tropical Indian Ocean (Nishikawa et al. 1985). The spawning season extends throughout the southern summer from about September or October to March at water surface temperatures in excess of 24°C. Once females start spawning, they appear to spawn daily. The Southern Bluefin is an asynchronous indeterminate spawner with annual batch fecundity 57 oocytes/g body weight. Fecundity of a 158 cm female with gonads weighing about 1.7 kg each was estimated at about 14–15 million eggs (Thorogood 1986, Caton 1994, Farley and Davis 1998, Schaefer 2001, Collette 2010). It is not known whether all mature fish spawn each year, every few years, or even only once in their lifetime.

In Australia, Southern Bluefin Tuna migrate along the west coast and across the Great Australian Bight and around Tasmania to 45°S, and then along the southeastern Australian coastline to about 30°S, off northern New South Wales.

The all-tackle game fish record is of a 167.5 kg fish caught off Tatra, Australia in 2009 (IGFA 2011).

This species is an important commercial species, especially off Australia. The meat is highly prized for the sashimi markets of Japan. A specialized fishery for sashimi-quality has been developed recently by New Zealand fishers.

This species has been intensively fished since the 1950s, primarily being taken on longlines, and the dramatic decline in the total population of Southern Bluefin Tuna to 7–15% of the 1960 parental biomass is well documented (FSC 2009). Canning was the most important form of local utilization of this highly esteemed fish until the early 1980s. This species is considered depleted by Majkowski (2007), and seriously overfished by Joseph (2009). If the current exploitation continues, it is estimated that the population will be below 500 mature individuals in 100 years. According the most recent stock assessment, there is no current sign that the spawning stock of this species is rebuilding (CCSBT 2009, CCSBT 2010).

This is a highly migratory species, listed in Annex I of the 1982 Convention on the Law of the Sea. Current worldwide catch quota has been reduced to 9,448 tonnes per year (CCSBT 2009). However, the current fishing capacity is much higher than the quota. There are several management measures in place including catch control, vessel monitoring, etc. However, more restrictions may be needed.

The CCSBT agreed that the status of the stock is at a critical stage and that a meaningful reduction in the total allowable catch (TAC) is necessary in order to recover the stock and work toward reaching an interim rebuilding target reference point of 20% of the original spawning stock. Consequently, the CCSBT reduced the global total allowable catch (TAC) for 2010 and 2011 to an average level over the two years of 80% of the previously allocated global TAC of 11,810 tonnes. Accordingly, the average global TAC for each of the 2010 and 2011 fishing seasons will be 9,449 tonnes.

The CCSBT has adopted a number of conservation measures including requirements for fleets to monitor and submit data to show compliance with TACs, development of scientific observer programs, monitoring of farming operations and port inspection of catches. The CCSBT has also implemented a Trade Information Scheme to collect more accurate and comprehensive data on Southern Bluefin Tuna fishing by monitoring trade and illegal, unregulated and unreported fishing.

Collette, B.B. and Nauen, C.E. 1983. FAO Species Catalogue. Vol. 2. Scombrids of the World: an annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date. Food and Agriculture Organization of the United Nations (FAO) Fisheries Synopsis number 125, volume 2.